In recent years, display devices such as electronic book readers have been actively developed. In particular, since a technique in which an image is displayed with the use of a display element having memory properties greatly contributes to reduction of power consumption, the technique has been actively developed (Patent Document 1).
In addition, a display device provided with a touch sensor has attracted attention. The display device provided with a touch sensor is called a touch panel, a touch screen, or the like (hereinafter also referred to simply as a touch panel). Further, a display device on which an optical touch sensor is mounted is disclosed in Patent Document 2.